Apparatus for calcining crude lithopone and other materials



frwmz af @a'jJam fi'ph Z Mam A. S. KREBS ill4 1 al Filed Apr igl APPARATUS FOR CALGINING CRUDE LITHOPONE AND OTHER MATERIALS May 11 1926.

Patented May 11. 1925.

UNITED STATES AUGUST SDNNIN KREBS, OF "WILMINGTON. DELAWARE, ASSIGNOR TO KREBS PIG- Mnivr & CHEMICAL COMPANY, DEL ARE.

OF NEWPORT, JEELAWAR-E, A CORPORATION OF APPARATUS FOR CALGINING CRUDE LITHOIPONE AND OTHER MATERIALS.

Original application filed April 14, 1923, Serial No. 632,045. Divided and this application filed June 21,

- 1924. Serial No. 721,436.

My invention relates to apparatus for calcining crude lithopone in carrying out the method of calcination which .forms the subject matter of my application filed 14 April 1923, Serial Number 632,045 of which this application is a division but While especially adapted to this use the apparatus can obviously be employed for the calcination of other materials.

In the manufacture of lithopone, purified liquors or solutions of barium sulphide and zinc sulphate are brought together in the precipitating or strike vats in the proper proportion and under proper conditions to produce a mixed precipitate of barium sulphate and zinc sulphide, which, after washingand more or less complete drying, constitutes what is known as crude lithopone.

Long experience in the manufacture of lithopone by old methods and apparatus and protracted experiments and testswith new methods and apparatus has demonstrated that a uniformly excellent product depends Very largely on the conditions ex isting during the calcination of the crude lithopone Which must be such that the mass under treatment in all its parts is uniformly heated and maintained at the necessary or desirable calcining temperature fora necessary period and these conditions have been found to require that the mass while being raised to and maintained at the necessary temperature should be constantly tumbled and mixed so that no portion remains in constant contact with or fixed relation to the Walls of the furnace chamber and all portions are exposed to the same heating conditions. It has also been found that for uniform good results it is highly desirable that the mass under treatment should for the most part be held out of contact with the furnace walls and for this and other reasons be maintained in a comparatively thick bed or layer in the furnace and for this and other reasons it has beenfound advisable to maintain in the rotating approximately horizontal mufiie, which it is preferred to use, a charge approximately half the cubic capacity of the muilie. In a rotating muflie through which the lithopone is fed this condition is conveniently maintained by providing the muflie With a centrally located outlet orifice of small diameter at its outer end. A further object prevent the adherence of particles of lithopone to the walls of the muffle furnace. Even where the muffle consists of a metal tube with smooth or unpolished inner walls there is a tendency for particles of lithopone to adhere to the wall, and consequently not mix with the bulk of the tumbling charge, consequently such particles become overburned and moreover such adhering particles tend to promote the adherence of other particles and cause the formation of overburned crusts. It has been found that the adherence of lithopone particles to the furnace wall can be prevented by causing vibrations to occur muffle at comparatively short intervals, such vibrations shake loosethe adhering particles and insure that all parts of the charge shall be calcined under similar and the best coin ditions.

Another object-of the invention is to pro vide a means for calcining lithopone by which the lithopone after having been raised to the necessary or'dcsirable temperature is permitted to soak in its own heat for -a period before its discharge from the inufiic, the lithopone being tumbled during this soaking period as it is during the heating up period.

Still another object of the invention is to provide for the cooling of the calcined lithopone before it is discharged from the muffle or an extension of the muffle, so as to lessen the tendency to form zinc oxide on the ex: posure of the hot lithopone to the air.

The nature of the invention will be best understood as described in connection with the drawing in which- Figure 1 is a longitudinal sectional clown tion of the improved furnace and Figure 2, a cross section on line 22 of Fig. 1, illustrating a convenient device for periodically rapping the metallic mutllc to cause vibration in its walls.

in the walls of the metal of my invention is to rotation by sion of the muflie C lying outside of furnace A, and having a heat insulating jacket F.

G is a delivery orifice centrally located in the end of the muflie tube and of small diameter. H is a hopper having a tubular delivery spout H in which, works a conveyor I, the shaft 1' of which has a sprocket wheel I secured to it. J is a sprocket.wheel secured to the muffle D. K is a driving shaft having sprockets K and K which, through chains L and L, drive sprockets I and J. M is a lever ivoted on shaft'K carrying on its freeen a weighted roller M which registers with the lifting cam N secured to the muflie, as shown in Fig.2.

stricted discharge opening 9; P is a belt conveyor for carrying away the calcined lithopone. Q and Q, are thermocouples. It indicatesthe level of the lithopone 1n the mufile.

In operation the' crude lithopone s chargedinto the hopper H and fed from this hopper into the recegipkg) end of the rotating mufile D by the indicated at I. The construction at the receiving end of the mufiie is such as to exclude air. The muflie D is kept in constant on to facilitate the travel of the lithopone through it. Ans /t he lithopone travels through the mufiie jit is gradually raised to proper calciningtemperature which it is whichthe lithopone is raised butwithin'themilar temperatures preferred the period of caicination will be in the neighborhood approximating a centrally located of from fiftyto twenty-five minutes, The lithopone is maintained in the rotating mufiie in a'compar'ativel-y deep layer orbed half the cubic capaclty of the mufile and this is best accomplished by providing thedeliveiziy end of the mufiie with elivery orifice of relatively small diameter, as indicated at G.

The exact proportion and volume of the lithopone to the cubic capacity of the muflle is not at all important so long as a bedor layer of substantial thickness is maintamedl The lithopone under treatment .is, in the shown, constantly stirred and apparatus tumbled by the rotation of the muiile and this tumbl ng action is of great importance n of the conveyor the described mechanism and ma be sh htly, inclined toward ,its, ,outer' in securin substantial uniformity of condition an exposure to heat of the whole mass of lithopone under treatment.

The tendency of particles of lithopone to adhere to the walls of the muiile and become overburned is overcome by causing frequent'vibrations in the walls of the metallic muflie and a convenient device for striking .frequent periodical blows causing such vi-,

brat-ion is the weighted lever M which is raised by the cams N and )eriodically allowed to fall upon the muffle l).

I have, as already stated, discovered that material advantages are secured by permitting the lithopone after it is raised to the desired calcining temperature to soak in its own. heat for a period before its final delivery out of the muffle. Such a heat soaking of the lithopone. is provided for in the O is an air cooled mufile extension havingexternal ribs 0' and a centrally locatedre- 4 apparatus shown by the mufiie attachment F iaving a heat'insulating jacket F which is attached to the mufiie outside of the furnace'Aso that, after being raised to the proper temperature the lithopone in the extension F 1s permitted to soak in its own pheric conditions existing in the muffle.

ThisI provide for by attaching to the end of the muffle a coolingextension indicated at O which, as shown, is intended to be air cooled and provide ribs Obut-which, of

course, can becpoled in any convenient way. This extensionyas shown, is secured to the end of the extension F and rotates with the muflie and is provided with a centrally located delivery orifice g of small diameter so.

that the conditions as to tumbling and thick 'ness of the layer are maintained in this ex'-' tension, In the construction shown the small dellvery orifice 'Gr 01' g insures not only that a properly deep bed of lithopone should be maintained but also provides against the entrance of air at the delivery end of the muflle and its extensions, 'aconlstant upward current of gas and vapors generated in the mufl'le passing through the small delivery orifices.

. lIav1ng now described my invention, what I rlaini as new and desire to secure by Letr ters Patent, i's

1.1L furnace for calcining crude lithopone and other material having a horizontal rotatable tubular ,mufile chamber and means for feeding lithopone through said muflie chamber in combinationwith means for externally heatingsaid muflle chamber located so as to apply heat to the front portion thereof but not to the rear portion ad- 90 heat while being constantly agitated and neeeeei. i

jecent'the delivery orifice and a heat insuiatother or delivery end of small diameter as ing cover for the rear unheated end of the compared with that of the cylindrical 10 mufiie tube. muffle and an externally cooled cylindrical 2. A furnace for calcining crude litho- 'muflie extension secured to the discharge 5 pone and other material comprising a rotatend of the muffleend having also a centrally able cylindrical mufide having means for located discharge opening of small diameter;- feeding crude lithopone at one end ands,

centrally located discharge opening at its v AUGUST SGNNIN KREBS 

